Despite the fact that only 1.5 percent of your body weight is calcium, it is not something to be taken lightly.

About 99 percent of that calcium is found in the bones and teeth; the rest is in the body cells and fluids where it is used for muscle contraction, blood pressure regulation, cell communication, blood clotting, release of neurotransmitters and other functions.

The roles of calcium are so vital to one’s survival that the regulatory mechanisms to maintain calcium are located inside and outside the cells. When calcium levels drop, parathyroid hormone is released to act to help increase blood calcium. When blood calcium levels become too high, the hormone calcitonin is released to inhibit the release of calcium in the blood.

When too little calcium is consumed in the diet the body can maintain normal blood levels by breaking down bone to release calcium. This process, called bone resorption, can provide a steady supply of calcium on a short-term basis. However, over time, a calcium deficiency can reduce bone mass.

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If low calcium intake occurs during the years of bone formation, the result is lower peak bone mass. If calcium intake is low after peak bone mass has occurred, bone loss may be increased and the risk of osteoporosis increases.

For most of North America the main source of calcium is dairy products. For those that don’t consume dairy products they can meet their calcium needs by consuming dark green vegetables, foods processed with calcium, fish consumed with bones, and foods fortified with calcium such as orange juice and breakfast cereal.

It is always best to attempt to get adequate nutrients from food, but if an individual can’t meet their calcium needs through diet alone there are many calcium supplements available. For young people supplements can increase peak bone mass, and for postmenopausal women calcium supplements can help reduce the rate of bone loss.

Whether your calcium comes from foods or from supplements an important consideration is the bioavailability.

The nutrient that most significantly affects calcium absorption is vitamin D. When calcium intake is adequate, calcium is absorbed into our cells by diffusion, but when intake is low, as is the case with most people, the absorption depends on the active form of vitamin D to help. When vitamin D is deficient, less than 10 percent of the calcium that is available will be absorbed. When vitamin D is adequate typically 25 percent is absorbed.

Calcium absorption is also affected by oxalates, phytates and tannins. Oxalic acid and phytic acid bind calcium and hinder its absorption.

You’ve heard that spinach is a great source of calcium. The problem is only about 5 percent of the calcium from this high-calcium vegetable is absorbed. The rest is bound by oxalates and ends up being excreted. Other vegetables that are good sources of calcium but that are low in oxalates include kale, collard greens, Chinese cabbage, mustard greens and turnip greens.

The bad news is that chocolate also contains oxalates, but the good news is that chocolate milk is still a good source of calcium because the amount of oxalates added to a glass of milk, from the chocolate, is small.

How much calcium do you need?

This list provides by age group the RDA (intake that covers needs of 97.5 percent of population) for calcium on a daily basis:

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Georgia Clark-Albert is a registered dietitian and adjunct nutrition instructor at Eastern Maine Community College who lives in Athens. Read more of her columns and post questions atbangordailynews.com or email her at GeorgiaMaineMSRDCDE@gmail.com.